Highly efficient estimation of entanglement measures for large experimentally created graph states via simple measurements

Quantifying experimentally created entanglement could in principle be accomplished by measuring the entire density matrix and calculating an entanglement measure of choice thereafter. Due to the tensor structure of the Hilbert space, this approach becomes unfeasible even for medium-sized systems. Here we present methods for quantifying the entanglement of arbitrarily large two-colorable graph states from simple measurements. The presented methods provide non-trivial bounds on the entanglement for any state as long as there is sufficient fidelity with such a graph state. The measurement data considered here is merely given by stabilizer measurements, thus leading to an exponential reduction in the number of measurements required. We provide analytical results for the robustness of entanglement and the relative entropy of entanglement

Impulse für das Biowaffenregime: ein provisorischer Compliance-Mechanismus als Schritt aus der Sackgasse

'Im Juli 2001 ist das Biowaffen-Übereinkommen (BWÜ) in eine Sackgasse geraten, denn die Verhandlungen über ein BWÜ-Protokoll scheiterten. Dies lag vor allem am Widerstand der USA, deren Haltung sich in absehbarer Zeit nicht ändern wird. Da ein Abkommen ohne ein effektives Überwachungs- und Kontrollsystem unwirksam ist, untersuchen die Autor/innen, wie die bis dato defizitären Compliance-Mechanismen des BWÜ gestärkt werden können. Auf der Grundlage einer Analyse des Überwachungs- und Kontrollsystems des Nuklearen Nichtverbreitungsvertrags (NVV) und des Chemiewaffen-Übereinkommens (CWÜ) sowie der bisherigen Erfahrungen der Vereinten Nationen im Umgang mit vermuteten Vetragsbrüchen entwickeln sie einen Vorschlag für einen vorläufigen, nicht institutionalisierten Compliance-Mechanismus. Der Vorschlag der Autor/innen besteht aus vier Elementen und erfüllt die Anforderungen, die an effektive Compliance-Prozeduren zu richten sind. Dazu gehört die Fähigkeit, Vertragsbrüche überhaupt zu erkennen, die nötigen Fakten zu sammeln und diese von unabhängigen Experten prüfen zu lassen. Zudem empfehlen die Autor/innen, dass zwischen den bisher verfügbaren Handlungsebenen eine weitere eingezogen wird. Bislang gab es nur die Ebene der relativ schwachen bilateralen Konsultationen und die der politisch aufgeladenen Diskussion im Sicherheitsrat. Beim provisorischen Compliance-Mechanismus sind Verhandlungen und Entscheidungen im Sicherheitsrat nicht notwendig, die bislang das entscheidende Hindernis für eine zügige Umsetzung des BWÜ waren. Der Vorschlag müsste lediglich die Entscheidungsprozesse in der Generalversammlung passieren. Somit könnte die Einhaltung des BWÜ bis zur Verabschiedung eines Protokolls kontrolliert werden und die Gefahr, dass das Regime durch Vertragsbrüche und Selbsthilfekonzepte unterminiert wird, würde noch rechtzeitig abgewendet.' (Autorenreferat

Quantitative verification of entanglement and fidelities from incomplete measurement data

Many experiments in quantum information aim at creating multi-partite entangled states. Quantifying the amount of entanglement that was actually generated can, in principle, be accomplished using full-state tomography. This method requires the determination of a parameter set that is growing exponentially with the number of qubits and becomes infeasible even for moderate numbers of particles. Non-trivial bounds on experimentally prepared entanglement can however be obtained from partial information on the density matrix. The fundamental question that needs to be addressed in this context is then formulated as: What is the entanglement content of the least entangled quantum state that is compatible with the available measurement data? We formulate the problem mathematically employing methods from the theory of semi-definite programming and then address this problem for the case, where the goal of the experiment is the creation of graph states. The observables that we consider are the generators of the stabilizer group, thus the number of measurement settings grows only linearly in the number of qubits. We provide analytical solutions as well as numerical methods that may be applied directly to experiments, and compare the obtained bounds with results from full-state tomography for simulated data.Comment: 7 pages, PQE 2009 special issu

Metamaterials proposed as perfect magnetoelectrics

Magnetoelectric susceptibility of a metamaterial built from split ring resonators have been investigated both experimentally and within an equivalent circuit model. The absolute values have been shown to exceed by two orders of magnitude that of classical magnetoelectric materials. The metamaterial investigated reaches the theoretically predicted value of the magnetoelectric susceptibility which is equal to the geometric average of the electric and magnetic susceptibilities.Comment: 5 pages, 3 figure

Modeling autosomal recessive cutis laxa type 1C in mice reveals distinct functions for Ltbp-4 isoforms

Recent studies have revealed an important role for LTBP-4 in elastogenesis. Its mutational inactivation in humans causes autosomal recessive cutis laxa type 1C (ARCL1C), which is a severe disorder caused by defects of the elastic fiber network. Although the human gene involved in ARCL1C has been discovered based on similar elastic fiber abnormalities exhibited by mice lacking the short Ltbp-4 isoform (Ltbp4S(-/-)), the murine phenotype does not replicate ARCL1C. We therefore inactivated both Ltbp-4 isoforms in the mouse germline to model ARCL1C. Comparative analysis of Ltbp4S(-/-) and Ltbp4-null (Ltbp4(-/-)) mice identified Ltbp-4L as an important factor for elastogenesis and postnatal survival, and showed that it has distinct tissue expression patterns and specific molecular functions. We identified fibulin-4 as a previously unknown interaction partner of both Ltbp-4 isoforms and demonstrated that at least Ltbp-4L expression is essential for incorporation of fibulin-4 into the extracellular matrix (ECM). Overall, our results contribute to the current understanding of elastogenesis and provide an animal model of ARCL1C.Peer reviewe

Modeling autosomal recessive cutis laxa type 1C in mice reveals distinct functions for Ltbp-4 isoforms

Recent studies have revealed an important role for LTBP-4 in elastogenesis. Its mutational inactivation in humans causes autosomal recessive cutis laxa type 1C (ARCL1C), which is a severe disorder caused by defects of the elastic fiber network. Although the human gene involved in ARCL1C has been discovered based on similar elastic fiber abnormalities exhibited by mice lacking the short Ltbp-4 isoform (Ltbp4S(-/-)), the murine phenotype does not replicate ARCL1C. We therefore inactivated both Ltbp-4 isoforms in the mouse germline to model ARCL1C. Comparative analysis of Ltbp4S(-/-) and Ltbp4-null (Ltbp4(-/-)) mice identified Ltbp-4L as an important factor for elastogenesis and postnatal survival, and showed that it has distinct tissue expression patterns and specific molecular functions. We identified fibulin-4 as a previously unknown interaction partner of both Ltbp-4 isoforms and demonstrated that at least Ltbp-4L expression is essential for incorporation of fibulin-4 into the extracellular matrix (ECM). Overall, our results contribute to the current understanding of elastogenesis and provide an animal model of ARCL1C.Peer reviewe

Efficient verification of quantum resources

In this thesis we present methods to efficiently verify quantum many-body experiments. The first part focuses on the quantitative verification of graph state experiments from simple measurements. In particular, optimal bounds on the fidelity, purity and entropy from stabilizer measurements are derived as well as high-quality bounds on entanglement measures. Furthermore, we show how entanglement may be quantified in spin and cold atom many-body systems using standard experimental techniques only. The scheme requires no assumptions on the state in the laboratory, and a lower bound to the entanglement can be read off directly from the scattering cross section of neutrons deflected from solid state samples or the time-of-flight distribution of cold atoms in optical lattices, respectively. Quantum mechanics offers many interesting properties such as entanglement and non-locality. However, one can easily think of more general correlations than quantum correlations. This gives rise to the question if quantum correlations are the most general allowed in nature? In the last part we propose a new axiom we call macroscopic locality. The idea behind this axiom is that any physical theory should recover classical physics in the continuum limit (i.e., when a large number of particles is involved and our measurement devices fail to resolve discrete particles). We will show that this very intuitive axiom, together with the no-signaling principle, allows to recover many important results in quantum mechanics, like the universality of the Tsirelson bound, or the set of accessible two-point correlators. Moreover, we will provide a complete characterization of the correlations between two distant physical systems that arise out of both axioms and comment on its consistency

Impact of Test Point Insertion on Silicon Area and Timing during Layout

This paper presents an experimental investigation on the impact of test point insertion on circuit size and performance. Often test points are inserted into a circuit in order to improve the circuit’s testability, which results in smaller test data volume, shorter test time, and higher fault coverage. Inserting test points however requires additional silicon area and influences the timing of a circuit. The paper shows how placement and routing is affected by test point insertion during layout generation. Experimental data for industrial circuits show that inserting 1% test points in general increases the silicon area after layout by less than 0.5 % while the performance of the circuit may be reduced by 5 % or more. 1

Combining deterministic logic bist with test point insertion

This paper presents a logic BIST approach which combines deterministic logic BIST with test point insertion. Test points are inserted to obtain a first testability improvement, and next a deterministic pattern generator is added to increase the fault efficiency up to 100%. The silicon cell area for the combined approach is smaller than for approaches that apply a deterministic pattern generator or test points only. The combined approach also removes the classical limitations and drawbacks of test point insertion, such as failing to achieve complete fault coverage and a complicated design flow. The benefits of the combined approach are demonstrated in experimental results on a large number of ISCAS and industrial circuits. 1